Everyone is at the least familiar with the Surefire X300 weapon light. It’s been around a long while now for something gun related. Recently they have come up with a upgrade on the old X300 with the 300U-A and B.
The A uses the old system and the B has the new T-slot with bolt to tighten with.
A much much better method if you are putting it on a 1913 rail.
Below is the older system and new compare.
Just be sure not to get over enthusiastic if you are tightening the new system on a polymer framed handgun.
One of the other very recent upgrades is boosting the light to 1000 lumen.